1. Field of the Invention
This invention relates to hard surfaced screw conveyors for centrifuges.
2. Description of the Prior Art
One of the principal maintenance problems with solids-liquid separating centrifuges has been due to wear of the helical conveyor blade by abrasive solids. Even though the conveyor blade be formed of hard wear steel alloys, abrasive solids, in some cases coupled with chemical attack, can cause such wear in the critical solids contacting area as intolerably to alter blade surface characteristics and clearance from the surrounding wall of the centrifuge bowl or basket. To save the expense of a new conveyor, it has been common practice to rebuild worn conveyors with hard surfacing materials to restore their requisite properties. However, this is a precision job, requiring special fixtures and often requiring return of the conveyor to the manufacturer for reworking, so that very considerable time and expense are involved.
To simplify conveyor blade renewal, conveyors have been made of a continuous helical steel blade to which are attached replaceable, contiguous, helical segments to form the working part of the conveyor. In one such construction, the segments have been steel alloy plates which are welded to the face and an end edge of the continuous blade. These segments are difficult to remove and difficult to replace, the latter requiring a conveyor gauge for accuracy of positioning. In addition, non-weldable, hard materials such as ceramics are more desirable in many cases. Segments of weldable or non-weldable materials have been bolted to the continuous blade to form its working area, but such attachment has not proved to be wholly satisfactory. Ceramic plates have been cemented in abutting relation to the face of the continuous blade, but suitable cements such as epoxy resin do not have sufficient strength to withstand radial forces at high gravities, and the cementing operation is difficult since the segments must be accurately held in position while the cement cures.
U.S. Pat. No. 3,764,062 discloses segments with a backing plate of weldable metal having a wear-resistant facing material bonded thereto by brazing, fusion or adhesive. The segments are attached in side-by-side relation to the continuous conveyor helix by welding along an edge portion overlying the face of the helix and along a second edge portion overlying the outer end face of the helix. Such segments are difficult to remove and replace in the field and the bonding of the facing material to the backing plate may not hold, particularly in high speed machines which develop high radial forces.